1. Field of the Invention
The present invention relates to a bonded wafer in which a polyimide is used as a joining agent, a process for producing the same, and a substrate using the same.
2. Description of the Related Art
Direct bonding, electrostatic joining, soot glass joining, etc. have been proposed as methods for producing a bonded wafer.
All these methods require a joining temperature exceeding 1,000.degree. C., and a joining time of several to several tens of hours.
Furthermore, all these methods require a production apparatus on a large scale, namely a heat treatment furnace to a diffusion furnace specification.
On the other hand, although an aromatic polyimide film is excellent in heat resistance, mechanical strength, electrical properties, etc., it shows poor adhesion to glass as is evident from the production of the film by casting on a glass support. The aromatic polyimide film has been considered inappropriate as a joining agent for the wafers.